Distribution of Soil Organic and Inorganic Carbon by Soil Taxa in the Central Eastern Pampas of Buenos Aires

Abstract

Carbon (C) pool records of different soil taxa and its vertical distribution are required because few studies have evaluated soil organic (SOC) and inorganic C (SIC) contents by horizon and by depth increment. Buenos Aires is an interesting area to characterize temperate agrosystem C stocks and could be used as a reference for temperate lands across the globe. Soil organic C and SIC are the largest reserve of C and have more than twice that of the vegetation or the atmosphere. The spatial distribution of soil C depends on climate, grain size, land use and landscape position, among others. Soil organic C fraction may affect the dissolution and leaching of native calcium (Ca) carbonate, resulting in a greater accumulation of SIC. Changes in C contents could have a great effect on its global balance. This study compared the storage of SOC and SIC in agricultural soil profiles at different depths and at different great group level in Buenos Aires. The analysis is based on 263 soil profiles. Major soil great groups were included (Argiudolls, Hapludolls, Natraquolls, and Haplustolls). Soil organic C and SIC (in kilogram per square meter [kg ⋅ m²]) were estimated for each soil taxa and profile (0- to 1- and 1.0-m depth). Argiudolls contained the most SOC in the first two horizons (A and B) compared with other soil groups. The mean content of total SOC (0–20 cm and at 20–100 cm) for the Argiudolls was significantly greater than in all other soil great groups; Natraquolls presented the least. The SOC presented a general pattern of progressive decrease with depth. Argiudolls presented the lowest SIC concentration and variability in the whole profile (0–100 cm). Natraquolls presented elevated SIC content. The SIC concentration in all groups followed a general pattern of gradual increase with depth. B and C horizons were the major contributors to SIC storage in the region. Haplustolls presented the highest total C storage (SOC + SIC). In all soil groups, the overall carbon storage (SOC + SIC) at a depth of 20 to 100 cm accounted for more than 50% in the whole profile. A partition in C storage among the most important Pampas soil great groups is feasible in the region conditions.